The need to cut long lengths of wood such as planks or logs into shorter pieces of equal length arises for a variety of reasons, including forming pieces of uniform length for construction purposes and cutting logs for firewood. Equal lengths are often important, both for the efficient utilization of the available source wood and for reasons related to the use that the wood will serve after it is cut, whether it be for firewood or for construction.
For cutting logs in particular, a chain saw is fast and economical, but there is no simple, fast, easy and practical way of measuring the length to which the wood is to be cut. Currently used methods for cutting logs to a given length with a chain saw include: (1) measuring out the desired length with a tape measure and marking the length thus measured; and (2) using a stick precut to the desired length as a measuring device and marking the length of the stick on the log.
Further methods appear in the patent literature, but none are practical. For example, U.S. Pat. No. 4,319,404 (Helmut E. Brock, Mar. 16, 1982) discloses a sighting device for attachment to a chain saw, the device consisting of a length of hollow tubing containing a wire and a mirror with a line painted on the mirror. The device is a cumbersome object that requires careful adjustment and is easily knocked out of adjustment. In addition, the operator's line of sight must be perfectly aligned with a view port on the device to achieve the proper cutting length. Another example is U.S. Pat. No. 4,561,186 (Arthur N. Keefe, Dec. 31, 1985), which discloses a tape measure attached to the bar of a chain saw by a magnet with pegs extending through the chain saw bar. Use of this device requires the purchaser to drill holes into the chain saw bar to receive the pegs. The tape measure when thus attached must clear the log being cut. As a result, the operator can only cut logs that fit within the space between the saw motor and the location of the tape on the saw bar. This prevents the operator from using the full length of the saw. Still another example is that found in U.S. Pat. No. 4,984,371 (Robert N. Frederickson, Jan. 15, 1991), which uses mirrors to gauge the length of the piece to be cut. The accuracy of the device is dependent on the angles of the mirrors and the relative position of the operator. Like the Brock device, this device is easily misaligned when knocked or bumped, which are highly likely to occur to any device that is mounted on a chain saw. It is unlikely that anyone cutting firewood would exercise the care required to operate this device successfully.